Digital electronic control systems are increasingly being used to control vehicle systems, industrial systems and other electro-mechanical systems and devices. For example, such digital electronic control systems are now found in a wide variety of on and off road vehicles, boats, aircraft and other forms of transportation, that typically use digital electronic control systems that include a digital control unit that is in communication with a plurality of sensors and drivers to monitor and control engine systems, steering systems, transmission systems, and/or fuel systems. Similarly, digital electronic control systems in the form industrial controllers are widely used, for example, in manufacturing facilities, chemical plants, air-conditioning systems, printing machines, computer numerical control devices and robotic devices.
The sensors that are usable with such a system can vary widely as can the types of sensor signals provided thereby. For example, different types of sensors can provide signals that have different signal range, different power characteristics, and/or physical connection requirements than those that the electronic control unit is adapted to receive. Such sensor provided output signals can take the form of analogue or digital signals and such sensor provided output signals can include signals characterizing information such as temperature, pressure, RPM and position. Thus, it is common in conventional digital electronic control systems to provide signal acquisition or conditioning circuits to match the signals provided by the sensors in the system to the requirements of the digital control unit used in the system. This circuitry varies according to the sensor type.
Similarly, the digital control units used in such systems do not often provide control signals that can be used to directly drive output devices. Typical output devices include, for example, heaters, solenoids, lamps and electrical motors. Accordingly, conditioning circuits are also provided between the digital control units and such output devices. These adapt the output signals from the digital control units to meet the particular needs of the output devices that they control.
The intensive use of such digital electronic control systems in vehicles and in industrial automation requires diagnostic testing methods in order to ensure correct operation. Conventionally, such diagnostic testing of digital electronic control systems is first done during the production process to verify that the systems perform as expected when compared with specified performance criteria. This is typically done using test fixtures that are specially adapted to this task. It will be appreciated that during production the digital electronic control unit, sensors and drivers have typically not yet been packaged within final enclosures and/or environmental protective systems and that it is comparatively simple to access testing points when these devices are in such a state.
After final manufacture, diagnostic testing can be performed as a matter of preventative maintenance or to diagnose the cause of error conditions. Such post manufacture diagnostic testing can be used to evaluate the operation of circuit elements, the functionality of a tested circuit in the system, in which the specific electronic circuit is installed, and/or to determine whether proper connections exist between the digital control unit and the sensors and/or output devices to which the digital control unit is connected.
Some conventional digital electronic control systems are adapted to facilitate diagnostics. For example, conventional automobile control systems are programmed to detect potential error conditions by analysis of data signals or other signals supplied by the sensors in the vehicle or by detecting that the sensor is not providing data. When such control systems detect these conditions, the digital electronic control systems provide signals that can be read by an appropriate reader connected to the automobile controller.
However, it will be appreciated that because such control systems are adapted to detect a data signal or other signals from a sensor, they are not particularly useful in detecting other conditions related to that sensor that might indicate that the sensor has a fault, that might indicate that a sensor is in a condition that suggests that a fault is imminent, or that might indicate that the electrical connection between the control system and the sensor has a fault. Accordingly, such an engine control module will typically provide only an indication that a fault exists and that the vehicle should be taken for service.
When this occurs, it is left to the service technician to use dedicated diagnostic testing equipment to detect such conditions so that the source of the fault can be determined. Unfortunately, this requires that the technician manually make appropriate diagnostic connections in order to detect signals that are of a different class than the sensor signals sensed during normal operation of the sensor but that indicate potential error conditions. This may involve connecting and disconnecting wiring harnesses or otherwise accessing sensitive electronic components thus risking damage to the components and/or wearing the components.
What is needed therefore is a digital electronic control system that facilitates diagnostic testing of the components of an electronic control system without requiring direct connections between an external device and the active components of a digital electronic control system. What is also needed in the art is a system for accomplishing this result while adding minimal expense and complexity to the overall digital electronic control system.